Since the first attempt to fabricate ion-exchanged glass waveguides by T. Izawa and H. Nakagome, "Optical waveguides formed by electrically induced migration of ions in glass plates", Appl. Phys. Lett., Vol. 21, p. 584, 1972, investigators have tried to obtain guidance by exchanging Na+ in glass by monovalent ions such as Li+ as described by T. Findakly, "Glass Waveguides by ion-exchange: a review", Optical eng., Vol. 24, p. 244, 1985; Ag+ as described by T. G. Giallorenzi, E. J. West, R. Kirk, R. Ginther and R. A. Andrews, "Optical Waveguides formed by thermal migration of ions in glass", Appl. Opt., Vol. 12, p. 1240, 1973; K+ as described by Y. H. Won, P. C. Jaussaud and G. H. Chartier, "Three-Prism loss measurement of optical waveguides", Appl. Phys Lett., Vol. 37, p. 269, 1980; Cs+ as described by V. Neuman, O. Parriaux and. L. M. Walpital, "Double alkali effect: influence on index profile of ion-exchanged waveguides", Electron, Lett , Vol. 15, p. 704, 1979; and Tl+ as described by E. Okuda, H. Wada and Y. Yamasaki, Paper Th86, Technical Digest of Topical Meeting on Integrated and Guided Wave Optics, Washington, D.C., 1984. Among these ions, K+, Cs+ and Ag+ are suitable for single-mode waveguide fabrication because of their small diffusion coefficient and index change in glass.